1. Field of the Invention
This invention relates to battery equalizing systems for chargeable batteries and, more particularly, it relates to battery equalizing systems adapted to be used with chargeable batteries of the type which can be charged rapidly and can afford a big discharge current when in use, including a system which equalizes the charging of each component cell of the battery during charging, as well as a system which, prior to charging, permits each cell to discharge so as to have the same residual charge left at the start of charging.
2. Description of the Prior Art
Recently there have been developed nickel-cadmium type cells and among them a nickel-cadmium cell with a relief valve for releasing internal gas in the event of overcharging. Such a cell has so low an internal resistance as to afford big discharge current (several amperes or more) and can be charged very rapidly (in a few or more minutes) when exhausted. For this reason, such cells are now being used as electric power sources for electrically driven toys such as electrically driven model airplanes as well as other various electric appliances.
In case of a battery assembly, however, which is composed of a plurality of such cells, and particularly in case the battery is used with repeated rapid charging and big-current discharging for a short period of time, it often happens that inverse charging may occur in some of the cells of the battery due to the slight difference in capacity or other characteristics among the individual cells and this often leads to a considerable shortening of the life of the battery as a whole.
The present invention is proposed to solve this problem and has for its object the equalization of the charging voltage across each component cell during charging as well as the avoidance of over charging of it. The charging equalizer circuit given in accordance with the invention may either be connected to the battery only at the time of charging or may normally be connected thereto in parallel in order to prevent any overcharging by mistake.
In one embodiment of the invention, a charge equalizing circuit is connected in parallel to each of the cells connected in series constituting the battery to equalize the amount of charging of each cell, while in another embodiment, a discharge equalizing circuit is connected in parallel to each of the cells connected in series so that, prior to charging, each cell may be discharged to a zero residual charge whereby to equalize the amount of the subsequent charging of each cell.